Chromosomes and Cell Division

DNA Limits Cell Size Cell cannot survive unless there is enough DNA to support the protein needs of the cell In some really large cells are multi-nucleated More nuclei = more DNA = quick, efficient protein manufacturing to meet large cell needs

Prokaryote Cell Division Bacteria Circular DNA Reproduce by binary fission = 2 daughter cells DNA copied Know steps

Cell Reproduction Cell division—making 2 new cells from 1 parent cell New cells are (and have to be) Genetically IDENTICAL Why? When? Who? How?

Eukaryotes —the Who Somatic cells—mitosis Growth & replacement of lost, dead or damaged

Cell Cycle S: "synthesis" DNA replicates; 2 copies G1: 1st growth phase major part S: "synthesis" DNA replicates; 2 copies S: "synthesis" DNA replicates; 2 copies G2: 2nd growth phase; microtubules made M: mitosis C: cytokinesis2 daughter cells

G1 checkpoint—cell growth—are conditions favorable to divide (yes—S phase; no—rest or stop) G2 checkpoint—enzymes edit and repair mistakes made during replication M checkpoint—triggers exit from mitosis to begin G1

I P M A T C I—I P—put M—my A—arm T—there C—’cuz

DNA double stranded negative charge wraps around histones (+ proteins) chromatid + centromere = chromosomes DNA

Chromosomes During mitosis Super-coiled DNA 46 in somatic (body) cells Contains 1000s of nucleotides Contains 100s of genes Small mistakes have major complications

Interphase Not mitosis… set up for mitosis centrioles replicate DNA replicates & condenses

Prophase Chromosomes 1st visible Centrioles move to poles & form spindle fibers Nuclear envelope breaks down

Prophase in plants… Spindle fibers Disappearing nuclear envelope Doubled chromosome

Metaphase "middle" centromere replicates Chromosomes line up along the equator

Metaphase in Plants… Centromere Sister chromatids

Anaphase chromatids pulled to poles Pulled by spindle fibers

Anaphase in Plants…

Telophase and Cytokinesis nuclear membrane reforms spindle fibers disassembles uncoiling of chromosomes cleavage; membrane pinches in

Telophase in Plants… Cell plate forms Nuclear envelope reappears Two daughter cells are formed

Differences in plants plants—cell plate forms have asters not centrioles

Plant Mitosis

Why is mitosis important? What’s its purpose? Growth and replacement of dead, lost and damaged cells Ensures each daughter cell gets an complete and exact copy of the genetic material from the parent cell in the quickest, most efficient manner

Mitosis